Does Recalibration Response Shift Alter Perceived Treatment Effects in Patient-Reported Outcomes After Anterior Cruciate Ligament Reconstruction?
Orthopaedic journal of sports medicine · 2026
Post-ACLR PROM change scores can be off by 3-18 points because patients' internal benchmark for 'normal knee' shifts after surgery.
The paper
Prospective cohort study, n=171 primary ACLR patients (mean age 24, 56% male), Level of evidence 2.
What they found
Adjusted change scores (accounting for patients' shifting internal reference point) were significantly greater than traditional unadjusted change scores for nearly every KOOS/IKDC subscale at 1 and 2 years (P <.05), except KOOS Sport at 1 year (P =.17). The gap between adjusted and unadjusted change ranged from 3 to 18 points, and three-quarters of participants showed a meaningful response shift on at least one PROM. Coping strategies and life events predicted patients' follow-up PROM scores, but they did not predict the size of the response shift itself, so the shift isn't simply a proxy for how well someone is coping or what else is happening in their life.
Study design
Prospective cohort study of patients undergoing primary ACL reconstruction, with KOOS and IKDC collected preoperatively and at 1 and 2 years, plus a retrospective ('then-test') re-rating of preoperative status at each follow-up to calculate response-shift-adjusted change scores. This sits below an RCT or comparative cohort on the evidence hierarchy since there is no control arm or comparator treatment, it is a within-patient measurement study, not a trial of an intervention.
Methodology
The core method, the then-test, asks patients to retrospectively rate their preoperative KOOS/IKDC at 1 and 2 years out and compares that recalled baseline to their original prospectively collected baseline; the gap defines the response shift. This is standard in response-shift research but is inherently susceptible to recall bias, patients reconstructing a worse-than-actual baseline to make current improvement feel larger, which the authors acknowledge they cannot fully separate from genuine recalibration. Attrition at 1 and 2 year follow-up matters too, since patients lost to follow-up are often those doing poorly, which would understate the true shift; the paper does not report an objective functional or imaging anchor to validate either change score against actual knee status. A clinician wanting to gauge whether the 3 to 18 point gap is real for a given case has no independent check available here, only the internal consistency of the self-report data.
The appraisal
The statistical significance is not really in question, the more interesting number is the 3-18 point magnitude, which for measures where 8-10 points is often cited as a minimal clinically important difference, is large enough to flip a patient from 'meaningful improvement' to 'no meaningful change' depending on which change score you trust. This is a measurement-science finding about how we interpret PROM trajectories, not a comparative or causal claim about treatment efficacy, so it doesn't tell you ACLR works better or worse than assumed, it tells you your yardstick may be bending.
The gap
There's no objective, non-self-report anchor (functional testing, imaging, return-to-sport status) to determine whether the adjusted or unadjusted change score better reflects actual knee function, so we don't know which number, if either, is closer to the truth. There's also a limitation baked into the method itself: 'adjusted change' relies on patients retrospectively rating their own preoperative state at 1 and 2 years out (a then-test). That's the standard way to quantify response shift, but it's also vulnerable to ordinary recall bias and whatever story a patient currently tells themselves about their recovery, not just a genuine shift in internal standards. The paper can't fully separate the two.
Landmark context
This builds on the Sprangers and Schwartz response-shift framework from the broader health-related quality of life literature, applying then-test methodology to ACLR-specific PROMs (KOOS, IKDC SKF) where it has not been well characterised before.
What to do Monday
This shouldn't change what you do with a patient in clinic on Monday, but it should make you more cautious presenting a raw KOOS or IKDC change score to a patient or in an outcomes report as the definitive story of their recovery, especially when scores plateau or dip against their own sense of progress.
In practice
This applies to any post-ACLR patient you're tracking with KOOS or IKDC over the first two years, and to athletes in the S&C system whose RTS readiness is partly judged on self-report. In clinic, stop reading a flat or dipping PROM trend at 6-12 months as proof the patient has stalled, ask what they're comparing themselves to now, a young athlete two years out is often rating against their current, more demanding idea of a normal knee rather than their pre-op self, which can hide real progress on paper. On the performance floor, don't gate return-to-sport progression on questionnaire trend alone, anchor it to something that doesn't drift with the patient's own recalibrating yardstick, limb symmetry on Single Leg Press or Single Leg Extension for quad strength and a Single leg jump for power, baselined early and re-tested at your usual checkpoints. The caveat: this doesn't make the PROM wrong and the strength number right, it means they're measuring different things and will sometimes disagree, so use both rather than picking one as the tiebreaker.
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